System and method for reducing air bubbles in a fluid delivery line

ABSTRACT

A method and pump that accurately senses air in a fluid delivery line pulses or activates and deactivates the air sensor(s) multiple times during the pumping phase of the fluid delivery cycle and can generate alarms based upon a single indication or a cumulative indication of air in the line. The pump can include multiple air sensors spaced along the delivery line so that the method can use the multiple signals therefrom to distinguish real moving air bubbles from false positives and/or air bubbles adhered to the inner wall of the line.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority based upon U.S. Provisional ApplicationSer. No. 60/957,024 filed Aug. 21, 2007, which is expressly incorporatedherein by reference in its entirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

TECHNICAL FIELD

The invention relates to medical pumps for delivering a substance, suchas a fluid to a patient. In particular, the present invention relates todetection of air in a fluid delivery line, such as within a line set,used with a medical pump, which reduces and/or prevents the creation ofair bubbles within the fluid delivery line.

BACKGROUND OF THE INVENTION

Modern medical care often involves the use of medical pump devices todeliver substances, such as fluids and/or fluid medicine to patients.Medical pumps permit the controlled delivery of substances to a patient,and such pumps have largely replaced gravity flow systems, primarily dueto the pump's much greater accuracy in delivery rates and dosages, anddue to the possibility for flexible yet controlled delivery schedules.

A typical positive displacement pump system includes a pump devicedriver and a disposable fluid or pumping chamber, defined in variousforms including but not limited to a cassette, syringe barrel or sectionof tubing. A disposable cassette, which is adapted to be used only for asingle patient and for one fluid delivery round, is typically a smallplastic unit having an inlet and an outlet respectively connectedthrough flexible tubing to the fluid supply container and to the patientreceiving the fluid. The cassette includes a pumping chamber, with theflow of fluid through the chamber being controlled by a plunger orpumping element activated in a controlled manner by the device driver.

For example, the cassette chamber may have one wall or wall portionformed by a flexible, resilient diaphragm or membrane that isreciprocated by the plunger and the driver to cause fluid to flow. Thepump driver device includes the plunger or pumping element forcontrolling the flow of fluid into and out of the pumping chamber in thecassette, and it also includes control mechanisms to assure that thefluid is delivered to the patient at a pre-set rate, in a pre-determinedmanner, and only for a particular pre-selected time or total dosage.

The fluid enters the cassette through an inlet and is forced through anoutlet under pressure. The fluid is delivered to the outlet when thepump plunger forces the membrane into the pumping chamber to displacethe fluid. During the intake stroke the pump plunger draws back, themembrane covering the pumping chamber pulls back from its prior fullydisplaced configuration, and the fluid is then drawn through the openinlet and into the pumping chamber. In a pumping stroke, the pumpplunger forces the membrane back into the pumping chamber to pressurizeand force the fluid contained therein through the outlet. Thus, thefluid flows from the cassette in a series of spaced-apart pulses ratherthan in a continuous flow.

A fluid delivery line, such as a polymer tube which is well known in theart, is used with the medical pump devices to deliver the fluid from afluid reservoir to the patient, such as through a catheter or needleconnected to the fluid delivery line. In one prior medical pump, themedical pump included an air sensing arrangement having a transmitterand receiver for sensing air and/or air bubbles in the fluid deliveryline. The transmitter is positioned within the pump at a location whichis adjacent to a first side of the fluid delivery line when the fluiddelivery line has been installed or mounted by a caregiver within themedical pump device. The receiver is positioned within the pump at alocation which is adjacent to a second and opposite side of the fluiddelivery line to the first side when the fluid delivery line has beeninstalled or mounted by a caregiver within the medical pump device. Thetransmitter transmits an ultrasonic signal which travels through thefluid delivery line, and which is received by the receiver on theopposite side of the fluid delivery line from the transmitter. Thesignal transmitted by the transmitter and received by the receiver ismodified or affected by the physical elements (the fluid delivery line,air within the fluid delivery line, fluid within the fluid deliveryline, etc.) the signal encounters between the transmitter and thereceiver.

In one medical pump system, disclosed in U.S. Pat. No. 6,142,008 to Coleet al., which is hereby incorporated by reference herein, while a motoractuates a pumping cassette, a controller controls the sampling by anair bubble sensor over a portion of the fluid delivery line. Thecontroller determines whether each sample is either 100% air or 100%liquid by comparing a sampled signal from air bubble sensor to apredetermined threshold that is a fixed percentage of a last readingthat was found to indicate the presence of liquid in fluid deliveryline. If the sampled signal is valid and below the predeterminedthreshold, the controller determines that the sample indicates thepresence of air. Conversely, if a valid sampled signal is above thepredetermined threshold, the controller determines that the sampleindicates the presence of a liquid in the distal tubing. The controlleraccumulates the volume associated with each sample as delta values usedto determine the total liquid volume and the total air volume.

In this medical pump system, each sample is a representativeapproximation of the unsampled portion of distal tubing that precedesthe current sampling, and the air sampling time intervals approximatethe unsampled time intervals. The controller must determine a samplingtime interval (in seconds) for continuous rotation of motor using aratio of the motor's output drive shaft. For example, if the pumpingcassette is pumping at high rates (e.g., 1000 ml/hr) and the samplingtime interval is less than 40 milliseconds, the controller must set thesampling time interval, for example to 40 milliseconds. Further, if thepumping cassette is pumping at low rates (e.g., less than 126 ml/hr),the sampling time interval is set at 32 milliseconds, based on the ratioand other factors. Ideally, the sampling time interval begins whenvalves in the pumping cassette open and the interval ends when thevalves close.

In this medical pump system, the controller turns off the power to airbubble sensor when the motor is not actuating the pumping cassette. Inother words, the controller shuts down power to the air bubble sensorbetween each actuation of the pumping cassette, but leaves power to theair bubble sensor on during the actuation. When controller turns thepower on to air bubble sensor, just prior to actuation beginning,approximately one millisecond of warm up time is needed before thesensor may be used. The controller checks the output signal from airbubble sensor for a false high when the associated amplificationelectronics are first turned on and when the transmitter of the airbubble sensor is not transmitting an ultrasonic pulse to the receiver ofthe air bubble sensor.

Equations are employed by controller for various functions, as describedin this patent, including control of air bubble sensor, such asdetermining an air bubble sensor sampling rate, which is dependent onthe flow rate and other variables. In addition, various logic flows areused to detect air in the fluid delivery line, and provide alarms whensufficient air is detected in the fluid delivery line. However, theseequations and logic flows are based on a theory of operation which keepsthe air bubble sensor powered on during the entire non-retractionportion or pressurization phase of each stroke.

Thus, it is a principal object of this invention to provide a medicalpump and a method of operating a medical pump to overcome thesedeficiencies. The present invention is provided to solve the problemsdiscussed above and other problems, and to provide advantages andaspects not provided by prior medical pumps.

As such, one object of the present invention includes reducing nuisancealarms.

One further object includes reducing dancing bubbles potentiallyresulting from ultra-sonic waves passing through the fluid deliveryline, by reducing the amount of air detection sensor usage during pumpoperation, while at the same time providing for reliable air detectionwithin the fluid delivery line.

One additional object includes reducing dancing bubbles potentiallyresulting from ultra-sonic waves passing through the fluid deliveryline, by reducing the amount of air detection sensor usage during thedelivery phase of pump operation, while at the same time providing forreliable air detection within the fluid delivery line.

One further object includes reducing bubble generation and/or smallbubble accumulation/conglomeration potentially resulting fromultra-sonic waves passing through the fluid delivery line, by reducingthe amount of air detection sensor usage during pump operation while atthe same time providing for reliable air detection within the fluiddelivery line.

One additional object includes reducing bubble generation and/or smallbubble accumulation/conglomeration potentially resulting fromultra-sonic waves passing through the fluid delivery line, by reducingthe amount of air detection sensor usage during the delivery phase ofpump operation while at the same time providing for reliable airdetection within the fluid delivery line.

One further object includes establishing robustness in the method andsystem of air detection using at least predetermined, adaptive and/ordynamic threshold selection according to empirical testing and/ordelivery conditions at the time of actual delivery (i.e. tube type,fluid used, temperature, etc.)

One additional object includes intelligent and/or adaptive placement(when/where) of the first and subsequent air detection sensor “ping(s)”based times and/or angles of rotation (hard times and/or angles, and/ordelays from a reference points) for one or more pumping mechanisms.

One further object includes using existing pump hardware technology andupdating the software code to implement the system and method of thepresent invention.

One additional object includes reducing nuisance alarms resulting fromdancing bubbles by, for example, using multiple air detection sensors todetect air bubbles in the fluid delivery line.

A full discussion of the features and advantages of the presentinvention is deferred to the following summary, detailed description,and accompanying drawings.

SUMMARY OF THE INVENTION

The present invention is directed to a medical pump with an improvedmethod for detecting air in a fluid delivery line using a medical pumphaving a first air detection sensor with a first transmitter and a firstreceiver. In one embodiment, the medical pump also has a second airdetection sensor with a second transmitter and a second receiver. Boththe first and second sensors are provided for sensing whether there isair in the fluid delivery line and the amount of air in the fluiddelivery line. As described in greater detail herein, one embodiment ofthe medical pump is provided in connection with a disposable pumpingchamber, such as a cassette or tube, for delivering a substance, such asa fluid, to a patient. The medical pump further includes a pump drivefor exerting a force on the pumping chamber to apply pressure on thesubstance. The medical pump also includes a pump drive position sensoroperatively connected to the pump drive for continuously sensing theposition of the pump drive. The medical pump further has a processor orprocessing unit in electronic communication with the pump drive, thepump drive position sensor and the first air detection sensor forproviding control of these elements and for receiving input informationto utilize in making various determinations and operating the medicalpump as provided herein. The medical pump further has a memory inelectronic communication with the processor. The memory can have storedtherein programming code for execution by the processor. The programmingcode, at least in part, generally carries out the method of the presentinvention.

In one embodiment, the method, and medical pump, includes starting afluid delivery cycle. Once the fluid delivery cycle begins, the medicalpump activates or provides power to the first air detection sensor aftera first predetermined cycle parameter value has been met. This and otherpredetermined cycle parameter values can be an amount of time that haspassed after the stroke cycle has begun, can be an angular distance thatthe pump drive has traveled, can be a linear distance that the pumpingchamber has moved, and/or some other time, distance or other parameterwhich spaces the activation of the sensor from the beginning of thestoke cycle or from some other reference point. In one embodiment, eachfluid delivery cycle or stroke includes a pressurization phase, apumping phase, and a retraction phase, as will be described in greaterdetail below. The medical pump then measures a first air content signalwhich is generated by the first air detection sensor. When a second orplurality of air detection sensors are used, the medical pump will alsomeasure a second or plurality of additional air content signals whichare generated by the second or plurality of additional air detectionsensors, although the measurements, detection and/or determinations forthe second or plurality of additional air detection sensors may beperformed after a predetermined or calculated (dynamic) delay, such as atime or distance delay. The medical pump then generates first (andsecond/a plurality of additional, when additional air detection sensorsare present) air content data from the first (second/plurality ofadditional) air content signal(s), such as by converting an analogsignal to a digital value or data representative of the signal measuredby the air detection sensor. The processor can receive a plurality ofsamples for each of air content signals and convert each of the samplesfrom an analog signal to a digital value. As used herein, the termsignal can be singular or plural, and one of skill in the art shouldunderstand that the plurality of samples can be taken from a singlesignal or a plurality of signals, for example the same signal atdifferent times, when reference is made to a “signal” or “signals.” Theprocessor can be arranged to average each of the samples for themeasured first air signals. The processor then deactivates the first(second/a plurality of additional) air detection sensor after measuringthe air content signal and after a second (third, etc., for the second,etc. air detection sensors) predetermined cycle parameter value has beenmet, such as a travel distance or time.

The medical pump further determines whether the air content data (or airdetection data) has met a first predetermined air threshold. Theprocessor sets the air in line counter to zero prior to measuring thefirst air content signal. In one embodiment, the first predeterminedthreshold being met represents that there is air in the fluid deliveryline. If the first predetermined threshold is met, in one embodiment,the processor increments an air in line counter. In one embodiment, thesize of the increment can be the stroke volume of one stoke of a pumpingcycle divided by three. The processor further determines whether the airin line counter has met an alarm threshold, and issues an air in linealarm if the alarm threshold has been met. The alarm threshold can beset by the manufacturer at the factory and/or modified by a caregiver orbiomedical engineer and/or can be configured as a downloadable druglibrary parameter that can be customized by the user for a particularclinical care area, pump type, pump software version, patient type(adult versus infant, for example), or drug. In another embodiment, ifthe first predetermined threshold is not met, the air in line counter isset to zero.

Within the same stroke, the processor reactivates the first(second/plurality of additional) air detection sensor(s) after a third(fourth, etc.) predetermined cycle parameter value has been met, such asa distance or time, as provided above, and as explained in greaterdetail below. The medical pump then measures a second air content signalgenerated by the first (second/plurality of additional) air detectionsensor(s) and generates second air content data from the second aircontent signal(s) (for each air detection sensor), in a similar manneras the first air content signal(s). The processor further determineswhether the second air content data (or air detection data) has met thefirst predetermined air threshold, and deactivates the first airdetection sensor after measuring the second air content signal and aftera fourth predetermined cycle parameter value has been met, such as adistance or time.

In one embodiment, the first and other predetermined cycle parametervalues can be relative to the start of the fluid delivery cycle, such asa time since the beginning of the cycle or stroke, or such as a distancethe pump drive has traveled since the beginning of the cycle or stroke.The second and other predetermined cycle parameter values can also berelative to the first and subsequent predetermined cycle parametervalues or relative to when (a time) or to a where (a location) suchvalues have been met.

In a further embodiment, the processor can control the pump drive tocause the pump drive to rotate or drive at a speed based on the deliveryrate set by the caregiver. The delivery rate and pump drive speedestablish a stroke speed. The number of samples measured and received bythe medical pump is independent of the stroke speed. Thus, the way inwhich the measurements are taken, including the number of samples takenof the air content signal is not dependent on the speed of the fluidmoving through the delivery line.

In an additional embodiment, the processor increments an air in linecounter when the first predetermined threshold is met. If the firstpredetermined threshold is not met, the processor will set the air inline counter to zero. This determination of whether the firstpredetermined threshold is met continues in a programmed loop. Each timethis determination is made the processor will store another air in linecounter value representing a “current” value of the air in line counter,which is proximate to each time that the step of measuring the first aircontent signal occurs. Thus, a plurality of stored air in line countervalues is created and stored. The processor further determines whethereach of the plurality of stored air in line counter values has met afirst predetermined air in line counter threshold. For each of theplurality of stored air in line counter values that has not met thefirst predetermined air in line counter threshold, the processor isarranged to set each such plurality of stored air in line counter valuesto zero.

The processor and programming code can also be arranged to establish acurrent cumulative air in line counter value. In one embodiment, thecurrent cumulative air in line counter value is established bydetermining a highest stored air in line counter value for each group ofcontinuous non-zero stored air in line counter values, and adding thehighest stored air in line counter value to a previously determinedcumulative air in line air counter value. The processor then determinesif the current cumulative air in line counter value has met a cumulativeair in line counter value threshold. If so, the processor issues acumulative air in line alarm. This determination can be performed over apredetermined cumulative time interval. When the fluid delivery cyclebegins, the predetermined cumulative time interval begins at thebeginning of the fluid delivery cycle. Over time, the predeterminedcumulative time interval shifts, with the oldest value dropping out whena new “current” value is determined and stored, in a “moving window” orfirst in/first out (FIFO) process.

As provided above, the medical pump can have additional air detectionsensors downstream, or upstream, from the first air detection sensoralong the fluid delivery line for detecting air in the fluid deliveryline. When a second (or plurality of additional) air detection sensor(s)is used, after the first predetermined cycle parameter value has beenmet, the medical pump measures a first air content signal generated bythe second (plurality of additional) air detection sensor(s). Theprocessor and programming code running therein are configured togenerate first air content data from the first air content signalgenerated by the second (plurality of additional) air detectionsensor(s). When two air sensors are used, the processor is furtherconfigured to determine when the first air content signal generated bythe first air detection sensor is measured to establish a first airdetection time. The processor is also configured to determine when thefirst air content signal generated by the second air detection sensor ismeasured to establish a second air detection time, and to determinewhether the difference between the second detection time and the firstdetection time has met a predetermined delay time. The predetermineddelay time can be dependent upon a fluid delivery line size, a deliveryrate, and/or a distance between the first air detection sensor and thesecond air detection sensor, as will be described greater detail herein.One of ordinary skill should understand that these principles and stepsalso apply to an embodiment where there are more than two air detectionsensors as well. In one embodiment, the processor is configured to setthe air in line counter to zero if the difference between the seconddetection time and the first detection time has not met thepredetermined delay time.

Continuing with a two sensor embodiment, if the difference between thesecond detection time and the first detection time has met thepredetermined delay time, the processor determines whether thedifference between the second detection data has met/not met apredetermined multi-sensor tolerance value. When the predeterminedmulti-sensor tolerance value is not met, the processor is configured toincrement an air in line counter, such by a stroke volume divided bythree, similar to one prior embodiment. Also similar to one priorembodiment, the processor determines whether the air in line counter hasmet an alarm threshold, and issues an air in line alarm when the alarmthreshold has been met.

In another embodiment, the processor is further configured to deactivatethe second air detection sensor, after measuring the first contentsignal generated by the second air detection sensor, and after thesecond predetermined cycle parameter value has been met. After a thirdpredetermined cycle parameter value has been met, the medicalpump/processor are also configured to reactivate the second airdetection sensor, measure a second air content signal generated by thesecond air detection sensor, and generate second air content data fromthe second air content signal generated by the second air detectionsensor. After measuring the second air content signal generated by thesecond air detection sensor and after the fourth predetermined cycleparameter value has been met, the processor is configured to deactivatethe second air detection sensor. The values of the third and fourthpredetermined cycle parameter cause the second air content signal to bemeasured prior to the end of the pumping phase of the delivery cycle.Again, one of skill in the art should understand that these principlesand steps also apply to embodiments which include more than two airdetection sensors.

Other features and advantages of the invention will be apparent from thefollowing specification taken in conjunction with the followingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

To understand the present invention, it will now be described by way ofexample, with reference to the accompanying drawings.

FIG. 1 is an illustration of one embodiment of a medical pump of thepresent invention, wherein a single air sensor is provided

FIG. 2 is an illustration of another embodiment of a medical pump of thepresent invention, wherein multiple air sensors are provided.

FIG. 3 is an exploded view of one embodiment of an air detection sensorand cassette receiver assembly of a medical pump of the presentinvention.

FIG. 4 is a flow chart of one method of operating one embodiment of themedical pump of the present invention, wherein single air in linedetection is provided.

FIG. 5 is a flow chart of one method of operating another embodiment ofthe medical pump of the present invention, wherein cumulative air inline detection is provided.

FIG. 6 is a flow chart of one method of operating a medical pumpaccording to the present invention, wherein single air in line detectionis provided for one multiple air sensor embodiment.

FIG. 7 is a graph of single air data over time from execution of theflow chart of FIG. 4.

FIG. 8 is a graph of cumulative air data over time from execution of theflow chart of FIG. 5.

FIG. 9 is a timing diagram that may be useful in the determination andevaluation of one possible set of “pulses” or “pings” for one pumpingcycle of the medical pump of the present invention.

DETAILED DESCRIPTION

While this invention is susceptible of embodiments in many differentforms, there is shown in the drawings and will herein be described indetail preferred embodiments of the invention with the understandingthat the present disclosure is to be considered as an exemplification ofthe principles of the invention and is not intended to limit theinvention to the embodiments illustrated.

A medical pump includes but is not limited to enteral pumps, infusionpumps, cassette pumps, syringe pumps, peristaltic pumps, or any positivedisplacement fluid pumping device for the delivery of fluidsintravenously or intra-arterially to a patient. Referring initially toFIG. 1, one embodiment of a medical pump 10 is provided in connectionwith a disposable pumping chamber, such as a cassette 12 or tube, fordelivering a substance, such as a fluid, to a patient. In variousembodiments of the medical pump of the present invention, the pumpingchamber is a portion of at least one of a cassette, a tube, and/or asyringe, depending on the type of medical pump. The medical pump 10provides a mechanism for adjusting an actual delivery of the substancebased on variations from nominal data used to estimate pump performance.A processing unit 30 is included in pump 10 and performs variousoperations described in greater detail below. An input/output device 32communicates with the processing unit 30 and allows the user to receiveoutput from processing unit 30 and/or input information or commands intothe processing unit 30. Those of ordinary skill in the art willappreciate that input/output device 32 may be provided as a separatedisplay device and/or a separate input device. A memory 34 communicateswith the processing unit 30 and stores code and data necessary for theprocessing unit 30 to calculate and output the operating conditions ofpump 10. The memory 34 stores a programming code 36 formed in accordancewith the present invention for processing data to determine and controlthe operating condition of the medical pump 10. A clock 37 is used tokeep time in the pump 10. The clock 37 is connected to the processingunit 30, and provides the processing unit 30 with time information forcorrelating data over time or conducting time sensitive activities. Anelectric motor 38 is controlled by processing unit 30 and is energizedby a power supply 40 to serve as a prime mover for rotatably driving ashaft 42 connected to the motor 38. The processing unit 30 orders themotor 38 to run at a constant speed or at different speeds, depending onthe motor being used and depending on the flow rate desired through thepump 10. The down-stroke or delivery portion of the stroke has the motor38 running directly from power supply 40. The up-stroke, retract or fillportion of the stroke is run at a voltage set by the processing unit 30,so that the retract times are varied by the processing unit 30, wherehigher desired flow rates require faster retract speeds. A pumpingelement 44, such as a plunger, is operatively associated with the shaft42. When energized, the pumping element 44 reciprocates back and forthto periodically down-stroke, causing pumping element 44 to press onpumping chamber 24, and expel fluid therefrom. On an up-stroke, pumpingelement 44 releases pressure from pumping chamber 24 and thereby drawsfluid from inlet port 14 into pumping chamber 24. Thus, the pumpingelement 44 intermittently pressurizes the pumping chamber 24 during apumping cycle. The power supply 40, the motor 38, and/or the pumpingelement 44 together, alone, or in some combination thereof, may beconsidered a pump drive for the purposes of the present specification.

The pump drive step value can be a time to drive the pump drive, alinear distance to drive the pump drive, an angular distance or degreefor the pump drive to travel, and/or some other travel value. The motorcan be driven at a constant rate or a variable rate. In one form of amedical pump 10 using a constant rate motor or motor drive, such a motordrive creates variable speed movement of the pumping element 44, such asa plunger, via a series of cams. However, as mentioned, a variable speedmotor or motor drive may be used to create constant speed pumpingelement movement, such as a constant speed plunger. The calculations,determinations and delivery scheme will change accordingly, as one ofordinary skill in the art would understand. Other parts and/or elementsmay also make up the pump drive, as one of ordinary skill in the artwould understand. In addition, parts of each of the power supply 40, themotor 38, the pumping element 44, and/or other elements can make up whatis referred to herein as the pump drive, with the understanding that thepump drive is controlled by the processing unit 30 for driving thedelivery of the substance to the patient through the use of the pumpingchamber.

A force/pressure sensor 46 is operatively associated with the pumpingelement 44 to detect the force or pressure exerted by the pumpingelement 44 on the pumping chamber 24. As shown in FIG. 1, the sensor 46can be directly connected to the pumping element and positioned in-linewith the pumping element 44, between the pumping chamber 24 and theshaft 42 of the motor 38. In this embodiment, the sensor 46 is the onlyforce/pressure sensor included in the medical pump 10, and operates tosense the force/pressure on pumping element 44 as well as to generate aforce/pressure signal based on this force/pressure. The force/pressuresensor 46 is in electronic communication with the processing unit 30 tosend the force/pressure signal to the processing unit 30 for use indetermining operating conditions of pump 10. One of ordinary skill inthe art will appreciate that the pressure sensor 46 may be a forcetransducer, strain gauge, or any other device that can operatively sensethe pressure or related force brought to bear on the pumping chamber 24by pumping element 44.

A position sensor 48 is operatively associated with the pumping element44 to directly or indirectly detect the position of the pumping element44. The position sensor 48 tracks each pumping cycle of pump 10 bydetecting the position of the pumping element 44 at each position withineach cycle. As shown, the position sensor 48 is associated with theshaft 42. The position sensor 48 generates a pump drive travel signal bydetecting the rotational position of the shaft 42. The position sensor48 is in electronic communication with the processing unit 30 to sendthe position signal to the processing unit 30. The processing unit 30utilizes this information in various ways, such as described in U.S.patent application Ser. No. 11/510,106, filed Aug. 25, 2006, entitledSystem And Method For Improved Low Flow Medical Pump Delivery, which ishereby incorporated by reference herein. One way includes associatingthe incoming force/pressure data with a particular travel value withinthe pumping cycle, such as a time, a linear distance, and/or rotationaldistance or angle of travel. One of ordinary skill in the art willappreciate that the position sensor 48 could alternatively track a camattached to the shaft 42 or the pumping element 44. Additionally, one ofordinary skill in the art will appreciate that the position sensor 48 asused herein includes but is not limited to mechanical indicators such aspivoting dial indicators, electronic switches, Hall Effect sensors, andoptical based position detectors.

In a preferred embodiment, the motor 38 is a brush DC motor with a 128count magneto-resistive encoder that is used in quadrature, for a totalresolution of 512 counts per motor revolution. Depending on the numberof motor shaft 42 rotations needed to perform a pump cycle, the cyclecan be divided into a very fine number of positions. For example, if ittakes 10 rotations of the pump shaft 42 to complete one pumping cycle orstroke (360 degrees in one embodiment), each cycle can be separated into5120 travel positions or values. Thus, in this example, the positionsensor 48 can provide information which allows for a resolution of 5120travel positions per cycle for the processing unit 30 to determineand/or utilize within other calculations and determinations.

One or more air sensors or air detection sensors 60 are operativelyassociated with the processing unit 30 for detecting air in the fluidline, such as in the outlet fluid line 22. The processing unit 30receives signals and/or data from the air detection sensor(s) 60. In oneembodiment of the medical pump 10, the air detection sensor(s) 60 ispressed against and is in physical contact with the exterior surface ofthe outlet fluid line 22 tubing. The power supply can provide power tothe air detection sensor(s) 60 (connection lines not shown), which isconfigured to excite the outlet fluid line 22 with ultrasonic waves togenerate and provide an analog signal to the processor. The analogsignal from the air detection sensor(s) 60 is converted to digital data,providing accurate air content data of air contained within the outletfluid line 22, as will be explained in greater detail below. In normaloperation, in general, this air content data falls within an expectedrange, and the processing unit 30 (and therein, as understood to aperson of ordinary skill) determine that proper fluid flow is inprogress. When the air content data falls outside the expected range, ingeneral, the processing unit 30 determines and indicates that improperair content is being delivered to the patient. As is explained ingreater detail herein, the processing unit 30 can control the airdetection sensor(s) 60 and make various determinations to moreaccurately detect whether improper air is within the fluid deliveryline, such as within the outlet fluid line 22.

FIG. 2 depicts an embodiment similar to that shown in FIG. 1. However, aspecific cassette 12 is depicted with the internal construction shown.In addition, a dual air detection sensor arrangement 80 is shown.

Specifically, as shown in FIG. 1, the cassette 12 may include an inlet14 and an outlet 16 formed in main body 18. An inlet fluid line 20couples the inlet port 14 on the main body 18 to a fluid source such asan IV bag or other fluid container. Similarly, an outlet fluid line 22couples the outlet port 16 on main body 18 to the body of a patient. Asshown in FIG. 2, an inlet valve 26 and outlet valve 28 are locatedwithin the main body 18. The pumping chamber 24 is connected in fluidflow communication between the inlet port 14 and the outlet port 16. Thepumping chamber 24 operates to meter fluid through the cassette 12. Theinlet valve 26 resides between inlet port 14 and the pumping chamber 24.Inlet valve 26 operates to physically open and close the fluidcommunication between inlet port 14 and pumping chamber 24. The outletvalve 28 resides between the pumping chamber 24 and outlet port 16.Outlet valve 28 operates to physically open and close the fluidcommunication between pumping chamber 24 and outlet port 16. The pumpingchamber 24, inlet valve 26, and outlet valve 28 are all operativelyassociated with the pump 10 to control the flow of fluid through thecassette 12. The cassette is a passive valve system requiringpressurization of the pumping chamber 24 prior to fluid delivery. Inletvalve 26 and outlet valve 28 react to the pressure of the pumpingelement 44 on the pumping chamber 24. In operation, a substance such asa fluid enters through the inlet 14 and is forced through outlet 16under pressure. The fluid is delivered to the outlet 16 when the pump 10compresses the pumping chamber 24 to expel the fluid. Additional detailsof this cassette and other details and information may be found in U.S.Patent Application Publication No. 2005/0214129 A1, published Sep. 29,2005, the entirety of which is hereby incorporated by reference hereinand made a part of this specification.

In the embodiment of FIG. 2, the force/pressure sensor 46 comprises apressure probe located at least partially within the pumping chamber 24of the cassette 12. The current signal from pressure probe isproportional to the force exerted on the pumping chamber 24 by thepumping element 44. As is also the case in FIG. 1, the force/pressuresensor 46 is the only force/pressure sensor included in the medical pump10, and operates to sense the force/pressure on pumping element 44 aswell as to generate a force/pressure signal to the processing unit 30based on this force/pressure. One skilled in the art will appreciatethat the present invention is applicable regardless of the type andlocation of the force/pressure sensor.

The medical pump 10 of the present invention provides a mechanism forcontrolling or adjusting an actual delivery of fluid based on variationsfrom nominal data used to estimate pump performance. The processing unit30 retrieves the operating condition programming code 36 from memory 34and applies it to the force/pressure and travel data received during apump cycle. The force/pressure data and travel data are processed by theprocessing unit 30. Sensing the force/pressure, for example, that thepumping chamber 24 exerts against the pumping element 44, and analyzingthat force/pressure data can determine various parameters for use in theoperating the medical pump. The processing unit 30 utilizes theseparameters in a closed loop cycle/stroke feedback system to determineand/or calculate delivery parameters. Additional information about thisand other embodiments of the medical pump 10 can be found within U.S.patent application Ser. No. 11/510,106, filed Aug. 25, 2006, entitledSystem And Method For Improved Low Flow Medical Pump Delivery, which ishereby incorporated by reference herein.

In addition, as shown in FIG. 2, a multiple air detection sensorassembly 80 is provided. In one embodiment the multiple air detectionsensor assembly 80 is a dual air detection sensor assembly. The dual airdetection sensor assembly 80 includes a first air detection sensor 90and a second air detection sensor 100. The first air detection sensor 90includes a first transmitter 82 and a first receiver 84. The second airdetection sensor 100 includes a second transmitter 86 and a secondreceiver 88. The first and second transmitters 82, 86 are positionedwithin the medical pump 10 at a location which is adjacent to a firstside of the fluid delivery line 22 when the fluid delivery line 22 hasbeen installed or mounted by a caregiver within the medical pump 10. Thefirst and second receivers 84, 88 are positioned within the medical pump10 at a location which is adjacent to a second and opposite side of thefluid delivery line 22 to the first side when the fluid delivery line 22has been installed or mounted by a caregiver within the medical pump 10.

The first and second transmitters 82, 86 each transmit ultrasonicsignals which travel through the fluid delivery line 22, and which arereceived by the respective first and second receivers 84, 88 on theopposite side of the fluid delivery line 22 from the first and secondtransmitters 84, 88. Each signal transmitted by the first and secondtransmitters 82, 86 and received by the respective first and secondreceivers 84, 88 is modified or affected by the physical elements (thefluid delivery line, air within the fluid delivery line, fluid withinthe fluid delivery line, etc.) the signal encounters between therespective pairs of first and second transmitters 82, 86 and receivers84, 88. The control of the first and second air detection sensors 90,100 as well as the use of the signals generated by these sensors will bedescribed in greater detail below with reference to FIGS. 4-6, as wellas other figures.

With continued reference to FIGS. 1 and 2, the memory 34 with theprocessing unit 30 and stores program code 36 and data necessary for theprocessing unit 30 to calculate and output the operating conditions ofmedical pump 10. The processing unit 30 retrieves the program code 36from memory 30 and applies it to the data received from various sensorsand devices of the medical pump 10. Specifically, the processing unit 30processes the data from the medical pump 10 to determine variousoperating conditions, including when there is proper flow of fluidthrough the cassette 12 to the patient, and if air bubbles are in thefluid delivery line, such as air bubbles entrained in the fluid leavingthe cassette 12. Once the operating condition has been determined, theprocessing unit 30 can output the operating condition to the display 32,activate the indicator or alarm, and/or use the determined operatingcondition to adjust operation of the medical pump 10.

Once the cassette 12 is fully seated correctly and pumping operationbegins, the array of pressure data is analyzed by the processing unit 30to determine proper flow of fluid through the cassette 12 to thepatient. In one use, the processing unit 30 uses this pressure signalfrom pressure sensor 46 to determine that the cassette is properlypressing on the pumping element 44 and activates the pumping element 44to begin pumping the cassette 12. Similarly, the processing unit 30determines the orientation and presence of cassette 12 by processingdata received from an orientation sensor (not shown). Where the cassette12 is incorrectly oriented (backwards or upside down, for instance),where there is no cassette at all, or where the cassette 12 is not fullyseated, the processing unit 30 determines that improper proper cassetteloading has occurred.

Additionally, once the processing unit 30 processes data received fromthe orientation sensor to determine the presence of a properly loadedcassette in an open carriage assembly, the processing unit 30 can beprogrammed to automatically close the carriage assembly after a givenperiod of time and without a direct user command. This can be performedmanually as well. The processing unit 30 communicates with thedisplay/input device 32 and allows the user to receive output fromprocessing unit 30 and/or input (data or commands) into the processingunit 30. When the cassette 12 is loaded into the open carriage assembly,a user accesses the display/input device 32 to command the medical pump10 to automatically close the carriage assembly. Likewise, a useraccesses the display/input device 32 to command the medical pump 10 toautomatically open the carriage assembly when the cassette 12 is to beremoved and/or replaced.

Referring to FIG. 3, an exploded assembly view illustrates thefunctional components of one carriage assembly 300, including oneembodiment of an air detection sensor assembly. Specifically, a pair ofair detection sensor carriers 302 including sensor heads 304 attached tothe near ends of air sensor arms 306. In one embodiment of the carriageassembly 300 of FIG. 3, one of the air detection sensor heads 304 is afirst transmitter 82 and one of the air detection sensor heads 304 is afirst receiver 84, which together define an air sensor 60 as describedabove in relation to FIG. 1. In another embodiment of the carriageassembly 300 of FIG. 3, one of the air detection sensor heads 304includes/mounts the first transmitter 82 and a second transmitter 86spaced from the first transmitter 82 along the length of the outletfluid line 22 (here axially or vertically) and one of the air detectionsensor heads 304 includes/mounts the first receiver 84 and a secondreceiver 88 similarly spaced from the first receiver 84 along the lengthof the outlet fluid line 22 to define a multiple air detection sensorarrangement 80, as shown in FIG. 2 and referred to above. The arms 306are pivotally secured to the base surface 310 at hinges, which eachcomprise a pin member 312 and a socket 314 for pivotally receiving thepin member 312. The arms 306 each have a cam slot 316 formed thereinthat receive cam posts 318 located on air sensor cam 320. An air sensoractuator 324 is associated with the air sensor cam 320 to open and closethe air sensor arms 306. Guide elements 328 extend from the base surface310 to guide the movement of both the arms 306 and the air sensor cam320. While FIG. 3 shows a single pair of air detection carriers 302 formounting the multiple sensor arrangement 80, one skilled in the art canappreciate that multiple spaced air detection sensor carriers 302 can beprovided on the arms 306. Alternatively, multiple arms 306, each with asingle air detection sensor carrier 302 can be used to mount a multiplesensor arrangement.

When the carriage assembly 300 is traveling to an open position, theprocessing unit 30 (not shown) activates the air sensor actuator 324(via power supply 40, not shown) to force the air sensor cam 320 inward,pivoting the arms 306 about the hinges and moving the sensor heads 304apart. When the carriage assembly 300 is traveling to a closed position,the processing unit 30 (not shown) activates the air sensor actuator 326to force the air sensor cam 320 to move outward, pivoting the arms 306about the hinges and moving the sensor heads 304 together. The cam slots316 can be designed to include a rapid travel zone where the cam slot316 profile is such that the arms 306 close rapidly until thetransmitter/receiver pairs 82/84 (and 86/88, where applicable) touch thefluid delivery line 22 (not shown). The cam slots 316 can also have acompression zone where the cam slot 316 profile is such that the arms306 are gradually compressed, as well as a “dwell” zone where each camslot 316 profile is straight and the arms 306 do not close further withadditional movement of air sensor cam 320. It will be appreciated thatthe air sensing aspects of the present invention are applicable to othertypes of medical pumps, including but not limited to syringe pumps,reciprocating plunger pumps and peristaltic pumps. For example, thecarriage loader can automatically load a syringe or section of tubingand the air detection sensors 60, 90, 100 on carriers 302 can sense airpresent in the syringe, tubing connected thereto, or a section of tubingnot associated with a syringe.

With reference to FIGS. 4-6, the operation of the air detection sensors60, 90, and 100 will now be described in conjunction with the processingunit 30 and the programming code 34 running therein, for detecting airin the fluid delivery line. The following description assumes that thecassette 12 has already been inserted and installed into the carriageassembly 300. To carry out detection of the air in the fluid deliveryline, in one embodiment, the processing unit 30 executes the programmingcode 36. Referring to FIGS. 4 and 5, the general execution of oneembodiment of the programming code 36 is shown for an air detectionassembly 80 having one or a first air detection sensor 60, 90 (shown inFIGS. 1 and 2). Reference is made to a second air detection sensor 100and respective components thereof, from time to time, when applicable tothe second air detection sensor 100, for ease of understanding alater-described multiple air detection sensor embodiment, such as forexample a “dual air sensor” embodiment shown in FIG. 6.

FIG. 4 shows a single air in line detection flow diagram. Specifically,block 400 represents the beginning of the method, which includes thepump drive, such as the motor 38 and/or the pumping element 44, in acycle start position. Most of the remaining blocks represent operationsof the programming code 36 which execute each time the processing unit30 loops through the programming code 36, until interrupted or a branchin the programming code 36 causes an action to occur. For ease ofpresentation, many intermediary steps and programming loops are notshown, many of which are either known to one of ordinary skill in theart and/or are incorporated by reference herein from anotherspecification.

Continuing, block 404 represents an operation of setting a firstpredetermined air threshold, either at set up time of medical pump 10 orsome time prior to fluid being introduced into the fluid delivery line22. Specifically, the processing unit 30 receives an analog signal fromthe first receiver 84 of the first air detection sensor 90 when theprocessing unit 30 knows that there is no fluid in the fluid deliveryline 22. This analog value is converted to a digital value representedby “ADC” (Analog to Digital Converted value) in FIGS. 4-6. As an aside,in one embodiment, each ADC value is an average of a plurality ofsamples taken proximate in time, to reduce errors in reading the analogvalues, such as taking eight (8) samples and averaging the samples toobtain an ADC value. Further, the analog value, which is a voltage, isconverted to a digital value within a digital range of 0 to 4095, forenhanced accuracy and ease of processing. This range is provided fordetermining the difference between air and fluid within the fluiddelivery line 22. In one embodiment, twelve bits of digital data areprovided by the air detection sensor 90, 100 for use by the processingunit 30, as described herein.

Continuing with block 404, to obtain the first predetermined threshold,an offset value, such as one hundred and fifty (150), is subtracted fromthe ADC value measured while no fluid is in the fluid delivery line 22,to reduce “false air” indications. The processing unit 30 can initiateand perform this calibration using a benchmark, as follows: the airdetection sensors 90, 100 return an ADC_(dry)>3350 with thetransmitter(s) 82, 86 turned off (dry measurement), even though theremay still be a fully primed macro bore tube within the air sensor(between the transmitter(s) 82, 86 and receiver(s) 84, 88. Theprocessing unit 30 then performs the same determination with thetransmitter(s) 82, 86 turned on (wet measurement “ADC_(wet)”). The airdetection sensor(s) return values which should comply withADC_(wet)<ADC_(dry)−400. This preferred offset of four hundred (400) wasempirically determined. Specifically, the selection of the ADC values(what constitutes mostly fluid or what constitutes mostly air based ondetection criteria) is based on averaging hundreds of test data fordifferent fluids, tube types, at different temperatures. Using a singlethreshold is done so that one technology solution can work acrossdifferent scenarios (i.e. this works at a 90% or greater confidencelevel), without the added expense of implementing a dynamicallyestablished threshold. In doing so, the robustness of the system may bereduced slightly and a higher margin of error may exist. One way toremedy this would be to dynamically select or determine unique (varying)thresholds for each type of tubing, temperature and/or medication(fluid) used. The information needed by the processor to make thisdetermination can be provided within a bar-code on a medication vial,delivery set (bag and tubing set). A drug (fluid)/tubing/temperaturelibrary could be stored within the pump, and/or stored and/or downloadedfrom a central server. The library could be built having an appropriateset of threshold for each tube type, fluid type, and/or temperature.This determination could also be performed by dynamically detecting ormeasuring the force/torque required to close in on the tube for themotor used to operate the air sensor arms. The pump could include athermal sensor to measure and create temperature information. Theseparameters would allow unique and/or shift-on-the-fly adjustment/dynamicgeneration of the thresholds, and would likely establish an even greaterrobustness, nearing or meeting a 100% confidence level.

During operation of the medical pump 10, the process utilizes certainpredetermined or dynamic values. Specifically, the dynamic threshold offirst predetermined threshold is the value with the transmitter disabledjust prior to delivery. The first predetermined threshold is stored inthe memory 34 for later use. This value can alternatively be obtained orset just after calibration of the medical pump 10 occurs, before fluidis provided into the fluid delivery line 22. Typical ADC values thatmight indicate air in the fluid delivery line 22 are between 3200 and up(theoretical max is 4095). Typical ADC values that might indicate fluidin the fluid delivery line 22 are between 500 to 3200. In general, lowADC values indicate a higher volume or percentage of liquid and high ADCvalues indicate a higher volume or percentage of air in the fluiddelivery line 22 adjacent the air detection sensor(s) 90, 100.

At block 408, the processing unit initializes an air in line counter,referred to as “Single Air Data” or “SAD” in the embodiment shown inFIG. 4, by setting the air in line counter to zero. Block 408 takesplace prior to determining if there is any air in the fluid deliveryline 22 or the taking of any “live” air detection sensor 90, 100measurements or readings. Prior to taking any measurements, no power isprovided to the first and second transmitter(s) 82, 86, and therefore,no ultrasonic signal is transmitted by the first and second transmitters82, 86 at the start of the delivery. It has been found that providing acontinuous transmission of an ultrasonic signal from the first andsecond transmitters 82, 86 through the fluid delivery line 22 canenhance air bubble creation and/or break up air larger bubbles intosmaller air bubbles, thereby aggravating air bubbles in the fluiddelivery line 22, and making the detection of air bubbles moredifficult. Thus, referring to block 412, the processing unit 30, andprogramming code 36 therein, continuously receives position informationfrom the position sensor 48 and determines an amount of time and/ordistance that the pumping element 44 has traveled since the beginning ofthe pumping cycle. As mentioned, each pumping or fluid delivery cycle or“stroke” includes a pressurization phase, a pumping phase, and aretraction phase, in the context of the embodiments of FIGS. 1 and 2.

The following provides a brief explanation of the pressurization phase,pumping phase, and retraction phase, and one embodiment to determine andtrack these phases, for a better understanding of the presentembodiment. At the beginning of a pumping cycle, the pump drive 42causes the pumping element 44 to advance toward and eventually apply aforce/pressure on the pumping chamber 24 (see FIGS. 1 and 2). The cycleor pump drive start position has a pump drive position value and/or atime value associated therewith, which is stored in the memory 34 by theprocessing unit 30 at the start of the cycle. The cycle begins at 0degrees, or Bottom Dead Center (BDC) in a cam embodiment, with thepumping element 44 applying a force/pressure to the pumping chamber 24 aminimal amount at this point. The start position of the pump drive, suchas the pumping element 44, is at 0 degrees. This begins thepressurization phase of the cycle. Empirical data has shown that thetrue end of the pressurization phase ranges from about 0 degrees toabout 30 degrees. However, determining the actual end of thepressurization phase and the beginning of delivery phase can bedifficult, and is one of the subjects of U.S. patent application Ser.No. 11/510,106, filed Aug. 25, 2006, entitled System And Method ForImproved Low Flow Medical Pump Delivery. During the pressurization phaseof the cycle, the pumping element 44 moves into the cassette 12 (whichmay be referred to as the pressurization stroke because fluid iscompressed in pumping chamber 24 of the cassette 12 in one embodiment)building force/pressure within the pumping chamber 24, while the outletvalve 28 remains closed. In one embodiment, the force/pressure providedby the pressure sensor 46 is tracked and various calculations can beused to determine when the pressurization phase has ended and when thedelivery phase has begun. In general, when the outlet valve 28 shown inFIG. 2 has opened, the delivery phase of the pumping cycle begins.

When the processing unit 30 makes the determination that the deliveryphase has begun, the processing unit 30 also determines and stores thetime and the linear and/or angular position of the motor 38 and/or thepumping element 44 in memory 34 for reference purposes, one or more ofwhich will be used in subsequent determinations by the processing unit30. In one embodiment, the effective delivery cycle or delivery phase ofthe pumping cycle is generally from about 30 degrees to 180 degrees ofthe rotation. However, since the processing unit 30 has determined whenthe end of the pressurization phase has occurred and the processing unit30 receives sensed position information of where the pump drive ispositioned, such as the rotary or stepper motor position information,the processor can determine how much additional travel is needed tocomplete the delivery phase of the pump cycle and utilizes thisremaining travel value to accurately control the delivery phase.

Once the processing unit 30 has made the necessary delivery parameterdeterminations, the processing unit 30 controls the driving of the pumpdrive, such as stepping of the pump motor 38, utilizing determinedparameters. When the processing unit 30 determines that the deliveryphase is complete, the processing unit 30 sends a signal to stop thepump drive from continuously driving the pump drive. When the effectivedelivery cycle is complete, the processing unit 30 causes the pump driveto be reset to the beginning of the next cycle. For example, in oneembodiment using a cam, the pump drive is driven for a predetermined orcalculated time to bring the pump drive to the beginning of the nextcycle. In particular, the effective delivery phase of the pump cycleends at 5 degrees short of Top Dead Center (TDC), or 175 degrees ofrotation, and a retraction or depressurization phase begins at 180degrees. The depressurization phase depressurizes the pumping chamber24, which occurs from about 180 to 210 degrees. During thedepressurization phase, the pumping element 44 moves out of the cassette12 (which is called the up-stroke, depressurization or inlet stroke) andthe force/pressure drops off. As the pumping element returns to itsinitial position, while the inlet valve 26 remains closed, negativepressure builds within the pumping chamber 24. A refill phase within theretraction phase begins when the negative pressure within the pumpingchamber 24 is sufficient to the open the inlet valve 26. During therefill phase, the pumping element 44 moves out of the cassette 12building negative pressure within the pumping chamber 24 sufficient toopen the inlet valve 26 and draw fluids into the pumping chamber 24. Therefill phase of the retraction phase occurs from about 210 to 360degrees, or Bottom Dead Center (BDC), which brings the pump drive to thebeginning of the next cycle.

Continuing with the embodiments shown in FIGS. 4-6, in the context ofthe above-described three-phase delivery cycle, the processing unit 30does not provide any power to the transmitter(s) 82, 86 and/or providesa signal to the transmitter(s) 82, 86, preventing the transmitter(s) 82,86 from emitting any ultrasonic signals necessary for the detection ofair in the fluid delivery line 22, during the pressurization phase andduring the retraction phase. Further, the processing unit 30 does notprovide any power to the transmitter(s) 82, 86 and/or provides a signalto the transmitter(s) 82, 86, preventing the transmitter(s) 82, 86 fromemitting any ultrasonic signals necessary for the detection of air inthe fluid delivery line 22, at the beginning of the delivery phase.After a first predetermined cycle parameter value has been met, theprocessing unit 30 activates or causes power to be provided to the firsttransmitter 82 of the first air detection sensor 90, and in a dual airsensor embodiment, to the second transmitter 86 of the second airdetection sensor 100. This and other predetermined cycle parametervalues can be an amount of time that has passed after the stroke cyclehas begun, can be an angular distance that the pump drive has traveled,can be a linear distance that the pumping chamber has moved, and/or someother time, distance or other parameter which spaces the activation ofthe sensor from the beginning of the stoke cycle or from some otherreference point. In the embodiment shown in FIG. 4, block 412 shows thatthe processing unit 30 is causing “Ping #1” to occur at or afterfifty-five (55) degrees of rotation of the pump drive 38, 42 from thebeginning of the pumping cycle. “Ping #1” represents the processing unit30 causing the first transmitter 82 to transmit ultrasonic signals andthe first receiver 84 receiving such ultrasonic signals. Thus, themedical pump 10 measures a first air content signal generated by thefirst air detection sensor 90. In the embodiments shown in FIGS. 4-6,the ping or ultrasonic signal transmission lasts for ten (10)milliseconds (ms) and eight samples are taken by the processing unit 30during the ping. After the ping is completed, the transmitter(s) 82, 86return to their previous deactivated operating state, with theprocessing unit 30 not providing any power to the transmitter(s) 82, 86and/or providing a signal to the transmitter(s) 82, 86, preventing thetransmitter(s) 82, 86 from emitting any ultrasonic signals necessary forthe detection of air in the fluid delivery line 22. In the three-phasedelivery cycle embodiment of the present invention, at least a pluralityof “pings” will be provided and spaced apart in an attempt to minimizebubble creation and dancing bubbles, yet at the same time detect bubblesin the optimal manner. Thus, determining how many and where to place the“pings” is significant. In one embodiment, the following steps can betaken to optimize the location of (when) the first ping occurs. Based onat least the disclosure within U.S. patent application Ser. No.11/510,106, filed Aug. 25, 2006, entitled System And Method For ImprovedLow Flow Medical Pump Delivery, a skilled artisan would know how todetect the end of the pressurization phase of delivery using a forcesensor, as provided therein. Thus, when the outlet valve of the cassette“cracks,” and the actual fluid delivery begins (end of pressurizationangle/beginning of the fluid delivery phase), the angle of shaftrotation or time at which this occurs can be used to locate thebeginning of the first “ping,” using an offset value (delay in angle ortime) from the beginning of the delivery phase. The location of another“ping” or other “pings” can also be based on the determination of thebeginning of the delivery phase, by a further offset value from thebeginning of the delivery phase, from the beginning/end of the prior“ping,” or some other reference point. With reference to pumpembodiments described herein and within the above-referenced patentapplication, the last “ping” within the delivery phase of pumping cycleshould end at or before 175 degrees of shaft rotation, since toward theend of the delivery phase, not much fluid is delivered (thus, there isnot much fluid movement). This approach can also be used in non-low flowembodiments and in other embodiments, such as at least the otherembodiments disclosed in the above referenced patent application.

The samples of the air content signal are at least briefly stored in thememory 34 and the processing unit 30 averages the samples of the aircontent signal to obtain a more reliable measurement. As will beexplained further below, in one embodiment, additional pings areprovided during the delivery phase. Specifically, one potentialcommercial embodiment includes additional pings at ninety-four (94)degrees (“Ping #2”) and at one hundred fifty-six (156) degrees (“Ping#3”) of rotation of the pump drive 38, 42 from the beginning of thepumping cycle. The pings can also be measured relative the beginning ofthe delivery phase (calculated or otherwise), or some other referencepoint. Block “A” or 416 represents a portion of the programming code 36which is performed for each ping of the air detection sensor(s) 90, 100,such as the ping at fifty-five (55) degrees in FIG. 4. Block A includesblock 420 and block 424. Block 420 represents a predetermined delay timewhich the processing unit 30 lets pass before collecting the samples ofthe air detection signals received by the processing unit 30 from thefirst air detection sensor 90, and from the second air detection sensor100 in the dual air sensor embodiment described below. The processingunit 30, the air detection sensors 90, 100, or some other hardwaredevice can generate air content data from the air content signal. Theanalog signal is converted to a digital value or data representative ofthe signal measured by the air detection sensor(s) 90, 100. Asmentioned, the processing unit 30 can receive a plurality of samples foreach of the air content signals, convert each of the samples from ananalog signal to a digital value, store the digital values and thenaverage the stored values. Alternatively, the processing unit 30 mayreceive already converted values as air content data, in digital form,and then store and average the digital samples. The average of thedigital samples can also be considered as air content data. FIG. 4refers to this averaged air content data as “ADC”. The flow then movesto block 424, which represents the averaging of the digital samples toobtain “ADC”.

The flow then moves to block 428, which is also a part of block A. Block428 represents the processing unit 30 determining whether the aircontent data (or air detection data) has met a first predetermined airthreshold. At block 428 in the embodiment shown in FIG. 4, theprocessing unit 30 determines whether “ADC” is greater than or equal tothe ADC threshold as previously determined or set at block 404. In oneembodiment, the first predetermined air threshold being met representsthat there is air in the fluid delivery line. If this determination isnot true, the flow moves to block 432. At block 432, the air in linecounter or “SAD” (Single Air Data) is set to zero. From block 432, theflow then moves to block 436, which represents the processing unit 30determining whether the medical pump 10 is at the end of the fluiddelivery, typically occurring when a predetermined about of fluid hasbeen delivered or provided by the medical pump 10 to a patient. If thefluid delivery is complete, the flow moves to block 440 and theprocessing unit 30 stops the delivery and the stops operation of themedical pump 10. If the fluid delivery is not complete at block 436, theflow then moves to block 444, which represents the processing unit 30determining whether the delivery phase of the pumping cycle is completeand whether the retraction phase of the pumping cycle has been reached.If the determination at block 444 is true, the flow then moves back toblock 412, for providing the next ping at the appropriate time/traveldistance within the delivery phase of the next pumping cycle. If thedetermination at block 444 is not true, the flow then moves to block448, which represents the medical pump 10 providing a “ping #2” and a“ping #3”. In one embodiment, “ping #2” is at ninety-four degrees and“ping #3” is at one hundred fifty-six degrees of rotation of the pumpdrive 38, 42 from the beginning of the pumping cycle. “Ping #2” and“ping #3” each represent the processing unit 30 causing the transmitter82, 86 to transmit ultrasonic signals and the receiver 84, 88 receivingsuch ultrasonic signals. Similar to “ping #1”, in one embodiment theping or ultrasonic signal transmission by the transmitter lasts for ten(10) milliseconds (ms) and eight samples are taken by the processingunit 30 during the ping. Block 444 also represents that after each pingis completed, the transmitter(s) 82, 86 return to their previousdeactivated operating state, with the processing unit 30 not providingany power to the transmitter(s) 82, 86 and/or providing a signal to thetransmitter(s) 82, 86, preventing the transmitter(s) 82, 86 fromemitting any ultrasonic signals necessary for the detection of air inthe fluid delivery line 22. Thus, the processing unit effectivelydeactivates the air detection sensor after measuring the air contentsignals and after a second predetermined cycle parameter value has beenmet for each “ping,” as shown by the combination of block A or 416 withblock 444. Effectively, block A or 416 and associated blocks 412, 444and 448 continue to execute through a plurality of pumping cycles, aslong as the delivery is not complete and as long as an air in line alarmthreshold has not been met. Thus, for each ping the processing unit 30activates or reactivates the air detection sensor(s) 60, 90, 100 after apredetermined cycle parameter value has been met, such as a distance ortime, as provided above. The medical pump 10 then measures an aircontent signal generated by the respective air detection sensor(s) 60,90, 100 and generates air content data from the respective air contentsignal(s), in a similar manner as the detection of prior air contentsignal(s). The processing unit 30 then, again, determines whether theair content data (or air detection data) has met the predetermined airthreshold, and deactivates the first air detection sensor(s) 60, 90, 100after measuring the respective air content signal and after a respectivepredetermined cycle parameter value has been met, such as a distance ortime.

Returning to block 428, as mentioned above, the processing unit 30determines whether the air content data (or air detection data) has metthe first predetermined air threshold, and in one embodiment, bydetermining whether “ADC” is greater than or equal to the ADC threshold.If the first predetermined air threshold is met, in one embodiment thisrepresents that there is air in the fluid delivery line. If the firstpredetermined threshold is met, the flow moves to block 452. Block 452represents processing unit 30 incrementing the air in line counter or“SAD.” In one embodiment, the processing unit 30 increments the air inline counter or SAD by the stroke volume of one stoke of a pumping cycledivided by three. Of course, the stroke volume can vary depending on thepump and the cassette used, but in one embodiment the stroke volume is75 uL so that the stroke volume divided by three is 25 uL. The flow thenmoves to block 456. Block 456 represents the processing unit 30determining whether the air in line counter or SAD has met a “single”alarm threshold. In one embodiment, the determination includesdetermining whether the SAD is greater than or equal to the single alarmthreshold. The alarm threshold is typically predetermined by themanufacturer at the factory and/or modified by a caregiver or biomedicalengineer and/or can be configured as a downloadable drug libraryparameter that can be customized by the user for a particular clinicalcare area, pump type, pump software version, patient type (adult versusinfant, for example), or drug. In one embodiment, the single alarmthreshold can be selected by a caregiver from a group having at leastthe choices of 50 uL, 100 uL, 150 uL, 250 uL and 500 uL. In thisembodiment, 50 uL is the lowest single alarm threshold that can beselected, and 250 uL is the default setting. Other values can be used aswell.

If the determination at block 456 is true, the flow moves to block 460.Block 460 represents the processing unit 30 issuing a “single” air inline alarm in response to the SAD value being greater than the singlealarm threshold in block 456. The flow then moves to block 464, whichrepresents the processing unit 30 stopping the fluid delivery. Block 468represents an interaction between the flow and blocks shown in FIG. 4and FIG. 6 with the flow and blocks shown in FIG. 5, as will bedescribed in more detail below.

In one embodiment described above, the processing unit 30 receives,stores in memory, and averages eight air content signals/data. Also asdescribed above, the processing unit 30 can control the pump drive 38,42 to cause the pump drive 38, 42 to rotate or drive at a speed based onthe delivery rate set by the caregiver. The delivery rate and pump drivespeed establish a stroke speed. However, in one embodiment, the numberof samples measured, stored and/or averaged by processing unit 30 isindependent of the stroke speed. Thus, the way in which the measurementsare taken by the processing unit 30 and programming code 36 runningtherein, including the number of samples taken of the air content signalis not dependent on the speed of the fluid moving through the deliveryline 22.

FIG. 5 shows a cumulative air in line detection flow diagram.Specifically, block 468 from FIG. 4 or FIG. 6 is the same as block 504in FIG. 5, which indicates that the SAD or air in line counter data isused as input for additional determinations, as will now be described.It should be understood that the logic and flow of FIG. 4 and/or FIG. 6can be taking place simultaneously with the logic and flow of FIG. 5,and vice versa. The flow moves to block 508, which represents that atthe beginning of a fluid delivery a time parameter is equal to zero, atleast theoretically. Instead of the time parameter being the numberzero, a real time of day and date (Julian or otherwise) can be storedand used as a reference point, but which is otherwise theoreticallyconsidered as zero for the purposes of the method of the presentinvention. Reference should also be made to FIGS. 7 and 8 for chartswhich show SAD values generated by the processing unit 30 and stored inmemory 34 over time, as well as “CAD” (Cumulative Air Data) valuesgenerated by the processing unit 30 and stored in memory 34 over time.Specifically, each time the above-determinations are made, theprocessing unit 30 will store another air in line counter valuerepresenting a “current” value of the air in line counter, which isproximate to each time the air content signal is measured and to eachtime the air content data is generated. Thus, a plurality of stored airin line counter values or plurality of SAD values is created and stored,and used as follows.

The flow then moves to block 512, which represents a continuous actionby the processing unit 30 of finding the maximum “SAD” values for eachstring of non-zero SAD values. In other words, for each string ofnon-zero SAD values, having at least one SAD value as a part of suchstring, the processing unit 30 continuously determines the maximum valuefor the string, or string maximum SAD, of all such non-zero SAD values.The flow then moves to block 516, which represents that the stringmaximum SAD value must meet a minimum value in order to be consideredrelevant and be considered as a string maximum SAD. In the embodimentshown in FIG. 5, all string maximum SAD values must be at least fifty(50), otherwise such SAD value is ignored. If an SAD value is ignored,then the processing unit 30 unit does not use the SAD value indetermining a Cumulative Air Data (“CAD”) or a cumulative air in linecounter value determination, described below. The flow next moves toblock 520, which represents the processing unit 30 determining whethertime elapsed since the fluid delivery began has met a predeterminedcumulative time interval. In the embodiment shown in FIG. 5, thepredetermined cumulative time interval is fifteen minutes, and thus, ifthe processing unit 30 determines that the elapsed time since the fluiddelivery began is greater than fifteen minutes, then the flow moves toblock 524. Otherwise, the flow moves to block 528, which represents theprocessing unit 30 determining the cumulative air in line counter valueor CAD value. In one embodiment, the processing unit 30 determines thepresent cumulative air in line counter value (CAD) by adding all of thenon-ignored, maximum air in line counter values (maximum SAD's) for eachstring (non-ignored and non-zero). At block 528, as opposed to block524, the processing unit 30 uses SAD values generated and stored in thememory 34 since the beginning of the delivery, also considered as timezero, to determine the CAD values for each determination, as long as thetime elapsed since the beginning of the delivery is less than fifteen(15) minutes, per block 520. On the contrary, at block 524, theprocessing unit 30 uses SAD values generated and stored in the memory 34over a predetermined cumulative time interval, which in the embodimentshown in FIG. 5 is the last fifteen (15) minutes of the fluid delivery,to determine the CAD value for each determination after the firstfifteen (15) minutes of the delivery has been exceeded, per block 520.Thus, when the fluid delivery cycle begins, the predetermined cumulativetime interval effectively begins at the beginning of the fluid deliverycycle. Over time, the predetermined cumulative time interval shifts,with the oldest values dropping out when new “current” SAD and CADvalues are determined and stored, in a “moving window” or first in/firstout (FIFO) process.

The following chart shows one example of values for ADC, the incrementfor SAD, SAD, SAD filtered (for maximum SAD), ignore volume less than 50uL volume (ignore all SAD filtered or maximum SAD values below fifty(50)), and CAD for each minute of one sixty-seven (67) minute fluiddelivery. In one embodiment, when the processing unit has determinedthat SAD should be incremented, the amount to increment SAD is thestroke volume divided by three or SV/3. The values in the followingchart assume a stroke volume of seventy-five (75) and an ADC thresholdof 3335.

Time Increment Ignore volume < (min) ADC for SAD SAD SAD filtered 50uLCAD 0 1041 0 0 0 1 1029 0 0 0 0 0 2 1029 0 0 0 0 0 3 995 0 0 0 0 0 41032 0 0 0 0 0 5 3335 25 25 0 0 0 6 3350 25 50 50 50 50 7 1054 0 0 0 050 8 1074 0 0 0 0 50 9 1159 0 0 0 0 50 10 1159 0 0 0 0 50 11 3400 25 2525 0 50 12 1078 0 0 0 0 50 13 1034 0 0 0 0 50 14 3450 25 25 0 0 50 153450 25 50 0 0 50 16 3500 25 75 75 75 125 17 1299 0 0 0 0 125 18 1299 00 0 0 125 19 1026 0 0 0 0 125 20 3340 25 25 0 0 125 21 3350 25 50 50 50175 22 1041 0 0 0 0 125 23 1009 0 0 0 0 125 24 984 0 0 0 0 125 25 984 00 0 0 125 26 1033 0 0 0 0 125 27 1103 0 0 0 0 125 28 3550 25 25 0 0 12529 3500 25 50 0 0 125 30 3550 25 75 75 75 200 31 3333 0 0 0 0 200 323600 25 25 0 0 125 33 3650 25 50 0 0 125 34 3650 25 75 0 0 125 35 356025 100 100 100 225 36 3333 0 0 0 0 225 37 3800 25 25 0 0 175 38 3800 2550 0 0 175 39 3900 25 75 0 0 175 40 3910 25 100 0 0 175 41 3920 25 125 00 175 42 3930 25 150 0 0 175 43 3940 25 175 175 175 350 44 3333 0 0 0 0350 45 3940 25 25 0 0 350 46 3940 25 50 50 50 325 47 3330 0 0 0 0 325 483940 25 25 0 0 325 49 3940 25 50 0 0 325 50 3940 25 75 0 0 325 51 394025 100 100 100 325 52 3333 0 0 0 0 325 53 3950 25 25 0 0 325 54 3950 2550 0 0 325 55 3950 25 75 0 0 325 56 3950 25 100 100 100 425 57 3330 0 00 0 425 58 3950 25 25 0 0 425 59 3950 25 50 0 0 250 60 3950 25 75 75 75325 61 3200 0 0 0 0 325 62 3950 25 25 0 0 275 63 3950 25 50 0 0 275 643950 25 75 75 75 350 65 3200 0 0 0 0 350 66 3965 25 25 0 0 350 67 397025 50 50 50 300Referring to FIGS. 7 and 8, the SAD and CAD values from this example areshown in graphical form over time within these two figures,respectively.

Referring back to FIG. 5, after both blocks 524 and 528, the flow movesto block 532, which represents the processing unit 30 determiningwhether any one of the cumulative air in line counter values have met acumulative air in line counter value threshold. In one embodiment, thecumulative air in line counter value threshold is set at one (1)milliliter (mL), and the processing unit 30 determines whether thecurrent CAD value is greater than one (1) mL, as shown in FIG. 5. Thisthreshold is a clinical requirement for an alarm to be issued. (As withthe SAD single alarm threshold and other thresholds described herein,the cumulative air in line alarm threshold is typically predetermined bythe manufacturer at the factory and/or modified by a caregiver orbiomedical engineer and/or can be configured as a downloadable druglibrary parameter that can be customized by the user for a particularclinical care area, pump type, pump software version, patient type(adult versus infant, for example), or drug.) If this determination hasbeen met, the flow moves to blocks 544 and 548, which represent theprocessing unit 30 issuing a cumulative air in line alarm and stoppingthe fluid delivery of the pump 10, respectively. If the currentcumulative air in line counter value has not met the cumulative air inline counter value threshold, the flow then moves from block 532 toblock 536, which represents the processing unit 30 determining whetherthe fluid delivery has been completed yet. If the processing unit 30determines that the fluid delivery has been completed, then the flowmoves to block 540, which represents the processing unit 30 stopping thefluid delivery of the pump 10. If the processing unit 30 determines thatthe fluid delivery has not been completed, then the flow moves to backto block 512 for continued cumulative air-in-line detection.

Referring to FIG. 6, a single air-in-line detection flow diagram isshown for a dual air detection sensor embodiment. The embodiment shownis FIG. 6 is specifically directed to a medical pump 10 of FIGS. 1 and 2having a first air detection sensor 90 and a second air detection sensor100, as shown in FIG. 2. The flow diagram of FIG. 6 generally followsthe flow of FIG. 4, as specifically indicated by use of the same blocknumbering for those blocks which are the same in FIG. 6 as in FIG. 4.For all such blocks in FIG. 6 which are the same as the blocks in FIG.4, it should be understood that functions which the processing unit 30,programming code 36, memory 34 and/or other components of the medicalpump 10 perform in relation to the first air detection sensor 90,including the first transmitter 82 and first receiver 84, are alsoapplicable to the second air detection sensor 100, including the secondtransmitter 86 and the second receiver 88, as suggested within the abovedescription of FIG. 4. However, some of the functional blocks within theflow diagram of FIG. 6 include some different and additional functions,designated by a “prime” after the same block number as in FIG. 4 and/ora different block number, as shown. Specifically, block 416′ representsa modified block “A” from FIG. 4 in that at least blocks 604 and 608have been added between blocks 428 and 452. In addition, block 448′represents that the block 448 is performed in relation to both the firstand second air detection sensors 90, 100, in addition to the otherfunctional blocks being performed in relation to both first and secondair detection sensors 90, 100.

Referring to block 428 in FIG. 6, similar to block 428 in FIG. 4, theprocessing unit 30 determines whether the air content data (or airdetection data) has met the first predetermined air threshold, and inone embodiment, by determining whether “ADC” is greater than or equal tothe ADC threshold. Generally, if the first predetermined air thresholdis met, in one embodiment this represents that there is air in the fluiddelivery line. However, in order to be sure that air is being detectedin the embodiment shown in FIG. 6, instead of the flow next moving toblock 452 if the first predetermined threshold is met, the flow moves toblock 604.

After the first or other predetermined cycle parameter value has beenmet, the medical pump 10 measures an air content signal generated by thesecond air detection sensor 100. Similar to and in addition to the firstair detection sensor 90, the processing unit 30 and programming code 36running therein are configured to generate air content data from the aircontent signal generated by the second air detection sensor 100. Theprocessing unit 30 is further configured to determine when the aircontent signal generated by the first air detection sensor 90 ismeasured to establish a first air detection time. The processing unit 30is also configured to determine when the air content signal generated bythe second air detection sensor 100 is measured to establish a secondair detection time. The processing unit 30 also determines whether thedifference between the second detection time and the first detectiontime has met a predetermined delay time. Block 604 represents oneembodiment of this determination. Specifically, the processing unit 30determines whether the time when the second single air detection or“SAD” detection takes place minus the time when the first single airdetection or “SAD” detection takes place is less than or equal to apredetermined delay time. In one embodiment, the predetermined delaytime is dependent upon the fluid delivery line 22 size, a delivery rate,and/or a distance between the first air detection sensor 90 and thesecond air detection sensor 100. Specifically, in one embodiment, thepredetermined delay time or T_(delay) is the expected delay when a realair bubble goes through the first air detection sensor 90, then goesthrough the second air detection sensor 100. This delay time iscalculated and varies based on the fluid delivery line 22 tubing size,the delivery rate and the distance between the air detection sensors 90,100. Assuming the use of a cassette 12 that holds nominally 75 uL offluid, in a fluid delivery line 22 of a macro bore tubing, 75 uLoccupies a 0.583″ segment of this type of tubing. Thus, at a deliveryrate of 250 mL/hr, 75 uL is being delivered every 1.08 seconds (0.075mL×3600 sec/250 mL=1.08 seconds). In other words, the speed of an airbubble is 0.583″/1.08 sec, which equals 0.54 inches/sec. Hence, for adistance of one (1) inch between the centers of each of the first andsecond air detection sensor 90, 100, an air bubble detected by the firstdetection sensor 90 should be seen by the second air detection sensor 90in 1.85 seconds after the first air detection sensor 90 detects the airbubble (1″×1.08 sec/0.583″=1.85 sec). It should noted that a macro boretube is likely the worst case in terms of time delay since it has thelargest inner diameter and it will take longer for an air bubble totravel through such a the fluid delivery line 22. Thus, using macro boretubing values within calculations is likely the safest set of assumptionvalues within ongoing determinations.

The spacing of the air detection sensor pairs, 82/84, 86/88 from oneanother can be different distances. In particular, one way to determineand set this distance includes the following process. In order to “test”a potential distance value, a value can be selected which maintains theair detection sensors as a part of the pump, yet does not cause the pumphousing or construction to become too large for commercialacceptability. This chosen distance or spacing value can beautomatically fed back to the software to allow the pump to determinewhether a true bubble is worth detecting. Specifically, for a given tubeID size, the air detection sensor pairs spacing, and delivery rate, thetime at which a real bubble will pass through each sensor pair can bedetermined parametrically, as provided above with reference to FIG. 9 aswell. In one commercially available pump made by the assignee of thepresent invention, dancing bubbles have been seen to oscillate within a0.5″ peak-to-peak range. Thus, a minimum spacing of 0.65″ between theair sensor pairs should be observed to at least account for potentialdancing bubbles. Failure to use this minimum spacing may void the designintent of adding extra sensors in series. A distance/spacing valuebetween 0.75″ and 1.0″ would also be effective, since this spacingincludes design margin as far as the “dancing bubble” coverage, andwould still allow several air detection sensor pairs to be stacked,based on the minimal increase in size to the pump. Distances valueshigher than 1.0″ can also be effective and commercially viable if pumpsize and costs associated therewith are not significantly increased as aresult in the increased distance/spacing value.

If the determination of block 604 is met, the flow moves to block 608.In one embodiment, a tolerance value can be added to the process flowand programming code 36 to factor in changes in an air bubble betweenthe first and second air detection sensors 90, 100. Specifically, ε is atolerance that can be used to compare a specific air bubble detected bythe first air detection sensor 90 and detected by the second airdetection sensor 100. ε can be set at zero to look for an exact matchbetween air bubbles detected by the first and second air detectionsensors 90, 100. However, one fifth of the stroke volume is a preferablevalue to use to factor in potential changes in the air bubble betweenthe two sensors 90, 100. Thus, as indicated in block 608, in oneembodiment, the processing unit determines if the difference between thesecond detection data has met/not met a predetermined multi-sensortolerance value.

In the embodiment shown in FIG. 6, when the predetermined delay time hasbeen exceeded or when the predetermined multi-sensor tolerance value hasbeen exceeded, at blocks 604 and 608, respectively, the flow moves toblock 432. Again, at block 432, in one embodiment, the processing unit30 is configured to set the air in line counter to zero. However, whenthe predetermined delay time has not been exceeded and when thepredetermined multi-sensor tolerance value has not been exceeded, atblocks 604 and 608, respectively, the flow moves to block 452. Again, atblock 452, the processing unit 30 is configured to increment the air inline counter, such by a stroke volume divided by three, similar to oneprior embodiment. Likewise, the flow then moves to block 456. At block456, the processing unit 30 determines whether the air in line counterhas met the alarm threshold, and issues an air in line alarm when thealarm threshold has been met.

Similar to one prior embodiment, in the embodiment shown in FIG. 6, theprocessing unit 30 is further configured to deactivate both the firstand second air detection sensors 90, 100 after measuring the first aircontent signals generated by the first and second air detection sensor90, 100, as exemplified in block 444 by turning the first and secondtransmitters 82, 86, respectively, off The sensors 90, 100 are turnedoff after each ping is complete, such as after a second predeterminedcycle parameter value has been met. Likewise, at the beginning of eachping, the processing unit 30 reactivates the first and second sensors90, 100, and further air content signals generated by the first andsecond air detection sensors 90, 100 are measured. The medical pump 10,such as through the processing unit 30, generates air content data orair content signals generated by the air detection sensors 90, 100 inthe additional pings. After one or more additional predetermined cycleparameter values have been met, the processing unit 30 deactivates theair detection sensors 90, 100. The additional predetermined cycleparameter values cause the air content signals to be measured prior tothe end of the pumping phase of the delivery cycle. Other features andaspects of the dual air detection sensor medical pump 10 embodiment canbe understood with reference the single air detection sensor medicalpump 10 and/or other portions of the present specification.

A skilled artisan should understand that the cumulative air in linedetection flow shown and described in relation to FIG. 5 is applicableto single and multiple air detection sensor pump embodiments.Specifically, as SAD values are generated for each air detection sensor,CAD values are also generated for each air detection sensor. Thus, theSADs or air in line counter data for each air detection sensor, assuggested by blocks 604 and 608, are used as input for CAD/additionaldeterminations. As previously mentioned, it should be understood thatthe logic and flow of FIG. 4 and/or FIG. 6 can be taking placesimultaneously with the logic and flow of FIG. 5, and vice versa, for amultiple air detection sensor arrangement as well. Thus, for each airdetection sensor the flow of FIG. 5 takes place. Thus, SAD values CADvalues are generated by the processing unit 30 and stored in memory 34over time. Specifically, each time the above-determinations are made foreach air detection sensor, the processing unit 30 will store another airin line counter value representing a “current” value of the air in linecounter, which is proximate to each time the air content signal ismeasured and to each time the air content data is generated. Thus, aplurality of stored air in line counter values or plurality of SADvalues is created and stored, for each air detection sensor, and used ina similar manner as a single air detection sensor embodiment, but foreach sensor.

With reference to at least FIG. 9, as briefly discussed above, a methodcan be used to determine where and for how long to place each “ping” fordetecting air within the fluid delivery line. Within this method, oneobject is to make sure that there is enough air detection “coverage.” Todo so, a set of calculations can be performed to determine how fast abubble of a particular size will travel through the fluid delivery lineand to verify that a selected arrangement of one or more “pings” will“find” or detect the bubble based on the location of the bubblethroughout the delivery phase of each stroke or cycle and the positionand duration of each “ping.” In other words, there should be enough“pings” (one or more) for the appropriate length and appropriatelyspaced apart to reduce the risk/probability of outright missing airbubbles while at the same time reducing nuisance alarms. As one example,in a microbore tubing, a 75 uL bubble is about 1.998″ long based ongeometry of the tubing. At a delivery rate of 1000 mL/hr (which is thefastest delivery rate for one embodiment of a commercial pump of theassignee of the present invention), each delivery phase of a stroke(i.e. the time it takes for 75 uL to move down the tube) takes:

[(0.075 mL/1000 mL)×3600 sec]/2=0.135 sec.

In this equation, a divide by two (2) operation is needed to obtain thedelivery phase time, which recognizes that half of the stroke is usedfor delivery and the other half is used to retract which doesn't involvefluid dispensing. Thus, 75 uL, on average, travels at a speed of:

1.998″/0.135 sec=14.8 ips (inches per second).

In addition, at a delivery rate of 1000 mL/hr, a constant motor speed of6000 RPM is used, which translates into a constant output shaft RPM of222.22 in view of a gear reduction of 27 to 1. At 222.22 RPM, 1333.33degrees of rotation per second is achieved. These calculations may beunderstood even better with reference to at least the disclosure withinU.S. patent application Ser. No. 11/510,106, filed Aug. 25, 2006,entitled System And Method For Improved Low Flow Medical Pump Delivery.

Referring to the details of FIG. 9, a timing diagram of one set of“pulses” or “pings” for one pumping cycle or stroke of a medical pump10, such as the medical pump 10 of FIGS. 1 or 2 is shown. Theinformation obtained and shown in FIG. 9 provides one example of whereto place each of the pings, and the above and other calculations can beused to assess the ping placement arrangement shown therein.Specifically, first, second and third pings 904. 908 and 912,respectively, are shown. The first pulse 904 begins at 5 degrees afterthe beginning of the delivery portion of pumping cycle and ends at 18.3degrees after the beginning of the delivery portion, in terms of angleof rotation of the pump drive. The second pulse 908 begins at 84 degreesafter the beginning of the delivery portion and ends at 97.3 degreesafter the beginning of the delivery portion, in terms of angle ofrotation of the pump drive. The third pulse 912 begins at 165.7 degreesafter the beginning of the delivery portion and ends at 179 degreesafter the beginning of the delivery portion, in terms of angle ofrotation of the pump drive.

The depiction in FIG. 9 does not factor in the pressurization phase ofthe pumping stroke. However, in a pump embodiment which includes aperiod of time in which movement of the fluid in the delivery lineeffectively stops, such as the pressurization phase within oneembodiment of the present invention, this should be factored into theplacement of the “pings.” In a pump embodiment including apressurization phase, the first ping 904 could take place after apredetermined angle of rotation, such as where there is high probabilitythat the pressurization phase is complete (cracking has occurred) andsuch as at a position that will reduce the risk of missing an actual airbubble. Alternatively, the first ping can be placed at a predeterminedangle or time after a calculated or determined end to the pressurizationphase and beginning of the delivery phase.

Additional analytical information is provided within FIG. 9, which canbe understood from at least some of the information provided above, andfrom the following. In one embodiment having a constant output shaft of222.22 RPM, for an air bubble to travel from zero degrees to 0.5degrees, it takes:

(0.5°-0°)/1333.33°/sec=0.000375 sec.

At 0.5°, the plunger has moved down by0.030″×(1-cosine(0.5°))=1.1423e-06 inch (where 0.030″ is the nominal camoffset). This equation is based in part on information and calculationsprovided in U.S. patent application Ser. No. 11/510,106, filed Aug. 25,2006, entitled System And Method For Improved Low Flow Medical PumpDelivery. The instantaneous plunger speed is defined as the totaldisplacement divided by the total cumulative time and at 0.5°:

1.1423e-06 inch/0.000375 sec=0.003046 ips

This can be translated into a linear position for the plunger, for eachangle. If this calculation is performed for angles from 0° to 180°, theaverage plunger speed at 1000 mL/hr is about 0.44 ips. A speed ratiobetween the bubble and the plunger can be defined as K, and calculatedas follows:

average bubble speed/average plunger speed=14.8 ips/0.44 ips=33.30

From these calculations, and based on the location and duration of theping, a determination of how much bubble length is exposed to the pingcan be performed, which assists in determining whether enough ping“coverage” exists. For example, in the first ping 904 in FIG. 9, whichextends from 5° to 18.3°, the average bubble speed is about:

(1.925 ips+7.280 ips)/2=4.603 ips.

The 1.925 ips and 7.280 ips are determined for each of the respectivedegrees for the first ping, as shown in FIG. 9, using the calculationsabove. Since each ping 904, 908, 912 in FIG. 9 is turned ON for 0.010sec, this translates into the following amount of a bubble being exposedto the first and subsequent pings:

(0.010 sec×4.603 ips)=0.046″

Thus, one object is to select the ping locations and ON time so as tomaximize the amount of bubble exposure to each ping. Preferably, one“ping” should be located where plunger and air bubble speed are at thehighest value. As shown in FIG. 9, air bubble speed increasessignificantly toward the midpoint of the delivery phase of the pumpingcycle. FIG. 9 specifically provides the air bubble speed at thebeginning and end of each pulse 904, 908, 912, and provides an “averagebubble speed” at the midpoint between each beginning and each end, andeach end and each beginning, of each pulse 904, 908, 912. For eachmidpoint, FIG. 9 also shows the average bubble length by visualmeasurements taken at each of these points. This then translates into anamount of “average bubble length not seen” as well for each airdetection sensor “OFF” interval and each air detection sensor “ON”interval. As shown, a total average bubble length seen can bedetermined. This information can further be used to determine whetherthe “tested” ping configuration has a low probability of not detectingone or more air bubbles.

It should be emphasized that the above-described embodiments of thepresent invention are examples of implementations, and are merely setforth for a clear understanding of the principles of the invention. Manyvariations and modifications may be made to the above-describedembodiment(s) of the invention without substantially departing from thespirit and principles of the invention. All such modifications areintended to be included herein within the scope of this disclosure andby the following claims.

1. A method for detecting air in a fluid delivery line using a medicalpump having a first air detection sensor, comprising the steps of:starting a fluid delivery cycle; activating the first air detectionsensor after a first predetermined cycle parameter value has been met;measuring a first air content signal generated by the first airdetection sensor; generating first air content data from the first aircontent signal; determining whether the first air content data has met afirst predetermined air threshold; deactivating the first air detectionsensor after measuring the first air content signal and after a secondpredetermined cycle parameter value has been met; reactivating the firstair detection sensor after a third predetermined cycle parameter valuehas been met; measuring a second air content signal generated by thefirst air detection sensor; generating second air content data from thesecond air content signal; determining whether the second air contentdata has met the first predetermined air threshold; and, deactivatingthe first air detection sensor after measuring the second air contentsignal and after a fourth predetermined cycle parameter value has beenmet.
 2. The method of claim 1 wherein the first predetermined thresholdbeing met represents a conclusion that there is air in the fluiddelivery line.
 3. The method of claim 1 wherein the steps of measuringthe first and second air content signals generated by the first airdetection sensor, respectively, and generating first and second aircontent data from the first and second air content signals,respectively, comprise the steps of: receiving a plurality of samplesfor each of the first and second air content signals; converting each ofthe samples from an analog signal to a digital value; and, averagingeach of the samples for each of the first and second air signals.
 4. Themethod of claim 1 further comprising the steps of: incrementing an airin line counter when the first predetermined threshold is met; settingthe air in line counter to zero when the first predetermined thresholdis not met; storing an air in line counter value representing a currentvalue of the air in line counter, proximate to each time that the stepof measuring the first air content signal occurs, to create a pluralityof stored air in line counter values; determining whether each of theplurality of stored air in line counter values has met a firstpredetermined air in line counter threshold; setting each of theplurality of stored air in line counter values to zero that has not metthe first predetermined air in line counter threshold; determining ahighest stored air in line counter value for each group of continuousnon-zero stored air in line counter values; establishing a currentcumulative air in line counter value, wherein each cumulative air inline counter value is established by adding the highest stored air inline counter value to a previously determined cumulative air in linecounter value; determining if the current cumulative air in line countervalue has met a cumulative air in line counter value threshold; and,issuing a cumulative air in line alarm if any one of the cumulative airin line counter values has met the cumulative air in line counter value5. The method of claim 1 for detecting air in the fluid delivery lineusing the medical pump having the first air detection sensor and asecond air detection sensor, further comprising the steps of: activatingthe second air detection sensor after the first predetermined cycleparameter value has been met; measuring a first air content signalgenerated by the second air detection sensor; generating first aircontent data from the first air content signal generated by the secondair detection sensor; determining when the first air content signalgenerated by the first air detection sensor is measured to establish afirst air detection time; determining when the first air content signalgenerated by the second air detection sensor is measured to establish asecond air detection time; and, determining whether the differencebetween the second detection time and the first detection time has met apredetermined delay time.
 6. The method of claim 5 wherein thepredetermined delay time is dependent upon a fluid delivery line size, adelivery rate, and a distance between the first air detection sensor andthe second air detection sensor.
 7. The method of claim 5 furthercomprising the step of: if the difference between the second detectiontime and the first detection time has not met the predetermined delaytime, setting the air in line counter to zero.
 8. The method of claim 5further comprising the step of: if the difference between the seconddetection time and the first detection time has met the predetermineddelay time, determining whether the difference between the first aircontent data generated by the second air detection sensor and the firstair content data generated by the first air detection sensor has met apredetermined multi-sensor tolerance value.
 9. The method of claim 8further comprising the step of: setting the air in line counter to zeroif the predetermined multi-sensor tolerance value has not been met. 10.The method of claim 8 further comprising the step of: incrementing anair in line counter when the predetermined multi-sensor tolerance valueis met.
 11. The method of claim 10 further comprising the step of:incrementing the air in line counter by a stroke volume divided bythree.
 12. The method of claim 11 further comprising the step of:determining whether the air in line counter has met an alarm threshold;and, issuing an air in line alarm when the alarm threshold has been met.13. The method of claim 5 further comprising the steps of: deactivatingthe second air detection sensor after measuring the first content signalgenerated by the second air detection sensor, and after the secondpredetermined cycle parameter value has been met; reactivating thesecond air detection sensor after the third predetermined cycleparameter value has been met; measuring a second air content signalgenerated by the second air detection sensor; and, generating second aircontent data from the second air content signal generated by the secondair detection sensor.
 14. The method of claim 13 further comprising thestep of: deactivating the second air detection sensor after measuringthe second air content signal generated by the second air detectionsensor, and after the fourth predetermined cycle parameter value hasbeen met.
 15. A medical pump for delivery of a substance through a fluiddelivery line connected to a pumping chamber, comprising: a pump drivefor exerting a force on the pumping chamber; a pump drive positionsensor operatively connected to the pump drive for sensing the positionof the pump drive; a first air detection sensor for sensing whetherthere is air in the fluid delivery line; a processor in electroniccommunication with the pump drive, the pump drive position sensor andthe first air detection sensor; a memory in electronic communicationwith the processor, wherein the memory comprises programming code forexecution by the processor, and wherein the programming code is adaptedto: start a fluid delivery cycle; activate the first air detectionsensor after a first predetermined cycle parameter value has been met;generate first air content data from a first air content signal measuredby the first air detection sensor; determine whether the first aircontent data has met a first predetermined air threshold; deactivate thefirst air detection sensor after the first air content signal ismeasured and after a second predetermined cycle parameter value has beenmet; reactivate the first air detection sensor after a thirdpredetermined cycle parameter value has been met; generate second aircontent data from a second air content signal measured by the first airdetection sensor; determine whether the second air content data has metthe first predetermined air threshold; and, deactivate the first airdetection sensor after the second air content signal is measured andafter a fourth predetermined cycle parameter value has been met.
 16. Themedical pump of claim 15 wherein the programming code is further adaptedto: increment an air in line counter when the first predeterminedthreshold is met.
 17. The medical pump of claim 16 wherein theprogramming code is further adapted to: increment the air in linecounter by a stroke volume divided by three when the first predeterminedthreshold is met.
 18. The medical pump of claim 17 wherein theprogramming code is further adapted to: determine whether the air inline counter has met an alarm threshold; and, issue an air in line alarmwhen the alarm threshold has been met.
 19. The medical pump of claim 15wherein the programming code is adapted to: increment an air in linecounter when the first predetermined threshold is met; set the air inline counter to zero when the first predetermined threshold is not met;store in the memory an air in line counter value representing a currentvalue of the air in line counter, proximate to each time that the stepof measuring the first air content signal occurs, to create a pluralityof stored air in line counter values; determine whether each of theplurality of stored air in line counter values has met a firstpredetermined air in line counter threshold; set to zero each of theplurality of stored air in line counter values that has not met thefirst predetermined air in line counter threshold; determine a higheststored air in line counter value for each group of continuous non-zerostored air in line counter values; establish a current cumulative air inline counter value for each group of continuous non-zero stored air inline counter values, wherein each cumulative air in line counter valueis established by adding the highest stored air in line counter value toa previously determined cumulative air in line counter value; determineif the current cumulative air in line counter value has met a cumulativeair in line counter value threshold; and, issue a cumulative air in linealarm if any one of the cumulative air in line counter values has metthe cumulative air in line counter value.
 20. The medical pump of claim15, further comprising a second air detection sensor, wherein theprogramming code is further adapted to: activate the second airdetection sensor after the first predetermined cycle parameter value hasbeen met; measure a first air content signal generated by the second airdetection sensor; generate first air content data from the first aircontent signal generated by the second air detection sensor; determinewhen the first air content signal generated by the first air detectionsensor is measured to establish a first air detection time; determinewhen the first air content signal generated by the second air detectionsensor is measured to establish a second air detection time; and,determine whether the difference between the second detection time andthe first detection has met a predetermined delay time.